Miniature electrical indicating instrument of the moving coil type with torsion elements under tension for supporting the coil



Oct. 15, 1968 G.'SEIBEL 3,406,340

MINIATURE ELECTRICAL INDICATING INSTRUMENT OF THE MOVING con TYPE WITH TORSION ELEMENTS UNDER TENSION FOR SUPPORTING THE COIL Filed April 13, 1964 4 Sheets-Sheet 1 Inventor GEORG SE/BEL 3,406,340 MOVING G. SEIBEL Oct. 15, 1968 MINIATURE ELECTRICAL INDICATING INSTRUMENT OF THE COIL TYPE WITH TORSION ELEMENTS UNDER TENSION FOR SUPPORTING THE COIL 4 Sheets-Sheet 2 Filed April 13, 1964 Inventor GEORG SEIBEL Oct. 15, 1968 G. SEIBEL 3,406,340 MINIATURE ELECTRICAL INDICATING INSTRUMENT OF THE MOVING COIL TYPE WITH TORSION ELEMENTS UNDER TENSION I FOR SUPPORTING THE COIL Filed April 15. 1964 4 Sheets-Sheet :5

Inventor GEORG SEIBEL Oct. 15, 1968 G SEIBEL 3,406,340

MINIATURE ELECTRICAL INDICATING INSTRUMENT OF THE MOVING COIL TYPE WITH TORSION ELEMENTS UNDER TENSION FOR SUPPORTING THE COIL Filed April 13, 1964 4 Sheets-Sheet 4 Inventor GEO/26 SE/BEL WWW; M144 7? Un wdh St t s Paw Q 3 40 340 Y t MINIATURE ELECTRICAL INDICATING IN-.- STRUMENT OF THE MOVING COIL TYPE ,WITH TORSIONELEMENTS UNDER TEN SION FOR SUPPORTING THE COIL 1 Georg Seibel, Dreieiclienhain, Hesse, Gerinany assignur to Scli'oeller &' C02, Frankfurt am MaimTGe'rmahy Filed Apr. 13,1964, 'Ser; No. 359,271 (llaims'priority, application Germany, Apr. 17,1963, Sch 33,122;-Dec; 11, 1963, Sch 34,309 Claims.-(Cl. 324 -154) ABSTRACT OF THE. DISCLOSURE A miniature electrical indicating instrument, of the moving coil"type, is disclosed as including a relatively elongated support base having'a pair of bracket" means secured in longitudinally 'spaced relation thereon' and 'eachhaving an upstanding relativelyresilient arm formed with an upwardly opening key hole slot. The moving coil includes a frame having a pair of substantially coaxial andoutwardly extending tongues, one at each end of its axis, with the tongues lying in a common axial plane and each having an aperture therethrough; This frame is positioned between the bracket arms;

A pairof relatively elongated and relatively narrow torsio'n elements are provided, each having a pair of clamping jaws" secured thereto, one" "at "each end thereof." The distance between the jaws of each pair is substantially equal to the axial distanc e" between a respective bracket arm and the apertureof the adjacent tongue. One jaw of 'eachpair'is engaged inth'e aperture of a tongue and the other is [engaged with the-"outer face of the'adjacent bracket arm with the torsion element inserted'thro ugh the key hole slot of the latter. The torsion elements are thus connected under tension between axially oppositeends of the moving coil frame and the' bracket arms, and

suspend the moving coil foroscillation about'its axis. A

'magneti'cst ructure on the baseis operately associated with themoving'coil. T A further feature of the disclosure is the provision of damping means inthe' form' of a receptacle on the base adjacent end of the frame, and having its interior formed as asector shape'slot concentric with'the frame axis and having a very small axial dimensiOnxThis receptacle contains a viscous damping liquid, and a substantially fiat tongue extends radially from the frame into the viscous liquid. The inner dimensions of the receptacle are so small that-the" surfacetension of'the viscous liquid on the surfaces inhibit loss of liquid in any angular position of the coil, and the surfaces of the tongue in contact with :the liquid are of a material which is not wettable by the viscous liquid. p

Background of the invention invention relates to miniature electrical indicating I instrument of the moving coil type.

3,406,340 Patented 15, I968 "Known miniaturized electrical in dicatiiig' ,instrurnents are substantially proportionate reductionsj'of standard sized .measuring instruments of themoving coil type, galvanoin'etr'type, or the like. Thoseminiatureinstruments of ther'novingicoil type usually include adamping frame, a moving coil of electrically conductivel' wire, spiral springs, jewel bearings, acentral or, core magnet, and a vane or pointer as' an index. Their design as'rniniature instruments is relatively expensive, both froir'i'the labor standpointand the material standpoint. Eor this reason, such miniaturized instruments are not economi- Cally practical for many applications, particularly those in 'which qualitative measurement is more importantthan accurately measured absolute values and a low initial cost.

An object of the present invention is to provide a miniature electrical indicating instrument of the moving coil type and which requires greatly simplified manufacturing and assembly operations whereby the instrument may be produced on apr oduction line by unskilled workers. I V i 7 Another object of the invention is to provide such a miniature electrical indicating instrument which has a relatively small internal power drain. t

A further object of the invention is to provide a miniature electrical indicating instrument of the moving coil type which is very insensitive to shock and vibration forces, is substantially unaffected by external fields, and provides a particularly clear indication. v

Yet a further object of the invention is to provide a miniature electrical indicating instrument which is free of disadvantages of prior art miniature electrical indicating instruments, particularly with respect to initial cost, reliability, and durability.

Still a further object of the invention is to provide a miniature electrical indicating instrument including novel and improved damping means. v

In accordance with the invention, the foregoing objects are obtained by suspending the moving coil on tensioned, relatively narrow torsion elements, such as straps or wires, extending axially from eachend of the coil to fixed support means. Preferably compression type clamping means are used to secure the ends of the tension elements into formations projecting axially from each end of the moving coil orits frame, and means are provided for limiting axial and lateral movement of these formationswhile permitting substantially. free oscillation or rotation of the moving coil. 4 i

In order to dampen the oscillations of a moving coil measuring system of the type formingthe subject matter of the invention, it usually would be necessary to resort to inductive damping devices. However, such inductive damping devices, as a rule, are not sufficient, at least not without greatly increased expense, 'to obtain a deadbeat of the system. 'In point suspending moving coil systems, it is known to obtain damping by the use of a drop of silicone oil in the'bearings. However, due to the nature of the tensioned torsion element suspension of the moving coil system of the present invention, av damping arrangement of this latter type ca'nnot be used as there is no place to hold an effective amount of a damping liquid on the axis of revolution.

Accordingly, and in further accord with the invention, a practically absolute deadbeat of the instrument is obtained by providing a tongue, extending radially from about the axis of rotation of the moving coil. This tongue is arranged to dip into a very small reservoir containing the damping liquid, with the dimensions of the reservoir being so small that the surface tension of the damping liquid will prevent escape of the liquid from the reservoir in any position of the moving coil. system.

For an understanding of the principles of the invention, reference is made to "the following description of typical embodiments thereof as illustrated in the accompanying drawings.

In the drawings:

FIG. 1 is a perspective view of a miniature electrical indicating instrument embodying the invention, with the casing or cover removed, and partially broken away;

FIG. 2 is a perspective view of a moving coil of the instrument shown in FIG. 1, with the moving coil being formed by a printed circuit;

FIG. 3 is a perspective view of a moving coil usable with the instlument of FIG. 1 and with the coil being a wire winding; 7

FIG. 4 is a perspective view, partially broken away, illustrating the assembly of a moving coil, such as shown in FIG. 3, with an index;

FIG. 5 is a perspective .view of the exterior of a. miniature electrical indicating instrument embodying the invention;

FIG. 6 is a partial perspective view of a moving coil instrument in accordance with the invention, with the moving coil of FIG. 2 and illustrating a novel damping means; and

FIG. 7 is a sectional view of the damping means of the moving coil suspension arrangement shown in FIG. 6.

Referring to FIG. 1, the meter mechanism shown therein is mounted on a support base or plate 1 of dielectric or insulating 'materialQThe mechanism includes a central or core magnet 2, secured to or mounted on base plate 1, and having circular or cylindrical lateral surfaces. Magnet 2 is magnetized radially of its cylindrical or circular lateral surfaces. Also mounted on base plate 1 is a horizontally oriented soft iron magnetic yoke 3 which has enlarged extremities 30! formed as magnetic pole faces or shoes, which are curved cylindrically to be substantially concentric with the center of curvature of the respective cylindrical lateral surfaces of magnet 2. A moving coil, generally indicated as 4, embraces magnet 2 and has portions disposed between the'c-u'rved lateral surfaces of magnet 2 and the pole pieces or enlargements 3a of magnetic yoke 3.

Coil 4 is shown more clearly in FIG. 2, wherein it is i-llustrated as comprising a thin, plane aluminum sheet or foil frame 4a serving to carry printed circuit windings 4b formed on both sides of both surfaces of frame 4a and insulated therefrom. The metal carrying frame 4a is also effective as an inductive damper for oscillations of coil 4. The axially extending side edges of coil '4 are bent so that they are V-shaped in elevation, and these axially extending surfaces are positioned in the air gap between magnet 2 and poles 3a of yoke 3. -By such arrangement of these lateral portions of coil 4a, the effective parts of the moving coil are superposed in these air gaps. Thus, the air gaps can be made very narrow even when using printed circuit coils.

An alternative form of moving coil is shown in FIG. 3 as a substantially rectangular frame having a winding 5, of electrically conductive wire, thereon. If the frame is made of plastic composition or dielectric material, it is advisable to provide the same, in a known manner, with metal damping sheets or the like. 7

Both coil frames have axial extensions in the nature of tongues 40 (FIG. 2) and 5a (FIG. 3), and each of 4 these extensions is substantially fiat and formed with a keyhole slot or opening therethrough as indicated at 4d in FIG. 2 and at 5b in FIG. 3. These keyhole slots or openings are arranged to receive compression clamping means for securing the ends of the tensioned torsion suspension wires or straps to the respective moving coil. The tongues 4c and Scare electrically connected to opposite terminalsof the windings 4b or 5, respectively.

Themeans for clamping the tensioned suspension wires or straps to the moving coil orits frame comprises. folded metal strips 6 embracingthe wires or straps as shown in FIG. 1, these folded metal straps being wedged into the keyhole slots to clamp the ends of wires or straps 7 and 8 to the moving coil, and to establish electrical connection between wiresand straps 7 and 8 and the ends'of the moving coil windings 4b or 5. p

The folded metal strip clamps also extend through keyhole slots in theupright portions of angular brackets 12 and 13 secured to base 1 adjacent the'opposite ends of magnet 6 and adjacent the radially extending portions of the moving coils 4 or 5. As best seen in FIG. 1, the clamping strapsf'6 as well as the reduced portions of the tongues 4c and 5a are extended within the circular portions of the keyhole slots in brackets 12 and 13, and the assembly of the tongues and clamps is rotatable in such circular portion with some clearance. However, only a limited amount of clearance or play is provided arid, in thismanner, any damage to the coil and its suspension means, due to transverse shocks and the like, is prevented, as the coils can oscillate laterally only by the play or distance between the tongues and clamping straps and the inner periphery of the circular portions of the keyhole openings in brackets 12 and 13. i

In order to protect the moving coil and the clamping straps from shocks directed axially of the meter assembly, the tongues are extended laterally between the brackets 12 and 13 and the moving coils. These lateral extensions have only a small clearance with the upright portions of brackets 12 and 13, so that the tongues can shift axially only a small amount, under axial shock, before they engage the upright portions of brackets 12 and 13. This prevents objectionable tensions or tension stresses on the suspension means 7 and 8 of the moving coils. The circular portions of the keyhole slots in brackets 12 and 13 can also be formed with projections or abutments which will limit the angular oscillation of the moving coils in either direction, thereby further preventing damage to the moving coil or its mounting.

The outer ends of straps or wires 7 and 8 are clamped in bent metal straps 9 which are inserted or wedgedvinto keyhole shape slots or openings in the upright portions of resilient sheet metal angle brackets 10 and 11 secured to base 1. By initially stressing or inwardly bending the upright portions of resilient metal brackets 10 and 11, the resultant'initial stress thereof will maintain tension on the straps or wires 7 and 8. By angular adjustment of clamping jaws 9, the moving coil can be set accurately in its zero position, after which the clamping jaws can be fixed in the adjusted position in any suitable manner as, for example, by cementing or gluing.

Referring to FIGS. 6 and 7, the partially illustrated moving coil thereof comprises a support 21 having coil windings 22 printed thereon in the same manner as described for the moving coil 4 shown in FIGS. 1 and 2. Also, the coil support bracket 21-has tongues 21a projecting axially therefrom and formed with keyhole-shaped slots into which metal strap clamping jaws 24 for the torsion suspension means, such as straps orwires 23, of the moving coil may be inserted. Immediately below the axis'of the moving coil, and/or below the strap or wire 23, there is an angle-shaped tongue 25 which is bent downwardly and which extends radially of the moving coil axis. Tongue 25 extends into a reservoir in a tank 26, thisreservoir being substantially segment or sector-shaped in elevation and concentric about the axis of themoving coil. The

reservoir is in the form of a very narrow slot, and this slot is filled with a viscous liquid 27 such as silicone oil. The slot is sufiiciently narrow, being 1 mm. or less, that the liquid is held therein by surface tension and thus will not escape from the slotjin any position of the moving coilsystem. Preferably, tongue25 is made of, or coated with, a material, such as tetrafluor-ethylene or shellac, which will not be wetted by the damping liquid. This prevents the damping liquid from creeping upwardly along the tongue and thus maintains a constant dampingv effect. The damping system shown in FIGS. 6 and 7 has the advantage that the amount of damping is easily adjustable and the further advantage that mechanical resonance vibrations of the moving coil, which may be externally induced, are prevented.

An electrical indicating instrument embodying the invention has the advantage that, despite its relatively small size, relatively large or prominent indication means of known types may be used therewith. For example, a paraxial beam pointed may be used. Alternatively, a cylindrically arcuate sheet 14 (FIG. 4) may be formed with an index and may be arranged to turn coaxially with the moving coil and to be visible through an elongated window or slot 16 in the casing of the instrument, such as shown in FIG. 5. The indicating means may be connected with the moving coil in any desired manner. In the event that the moving coil has a support frame of dielectric or electrical insulation material, such as shown in FIGS. 3 and 4, the cylindrically arcuate sheet 14 may be formed of magnetically neutral metal and to have flaps which are inserted into the moving coil on the inner surfaces of the later-a1 longitudinally extending sides thereof. These fiaps, when so used, in addition to securing the cylindrical indicator sheet in position, serve further as inductive damping means.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

1. A miniature electrical indicating instrument of the moving coil type comprising, in combination, a relatively elongated support base; a pair of bracket means secured in longitudinally spaced relation on said base and each having an upstanding relatively resilient arm formed with an upwardly opening key hole slot said slots being substantially coaxial; a moving coil element including a frame having a pair of substantially coaxial outwardly extending tongues, one at each end of its axis, the tongues lying in a common axial plane and each having an aperture therethrough; the spacing of said bracket arms being substantially greater than the axial distance between said tongue apertures, and said moving coil element being positioned substantially midway between said brackets; a pair of relatively elongated and relatively narrow torsion elements each having a respetcive pair of clamping jaws secured thereto, one at each end thereof; the distance between the clamping jaws of each pair being substantially equal to the axial distance between a respective bracket arm and the aperture of the tongue nearest to the latter; one clamping jaw of each pair being engaged in the aperture of a respective tongue and the other being engaged with the axially outer face of the adjacent bracket arm with the associated torsion element inserted into the key hole slot of the latter, whereby said torsion elements are connected under tension between respective axially opposite ends of said frame and the respective bracket arms, said torsion elements extending substantialy coaxially of said moving coil element and suspending the same for oscillation about its axis; and a magnetic structure on said base operatively associated with said moving coil element.

2. A miniature electrical indicating instrument of the 6 moving coil type, as claimed in claim 1, including means fixed relative to saidbase and cooperable with said tongues to restrict lateral and axial displacement. of said moving coil element caused by external shocks and the like. 1

3. A miniature electrical indicating instrument of the moving coil type, as claimed in claim 1, in which each of said torsion elements is electrically conductive andhas its inner end in electrical connection with a respective opposite end of a coil forming part of said moving coil element; whereby said torsion suspension elements serve as current conducting leads for said moving'coil.

4. In a miniature electrical indicating instrument oftlie moving coil type, as claimed in. claim 1, oscillationdamping means operatively associated withsaid moving: coil element.

5. In a miniature electrical indicating instrument of the moving coil type, as claimed in claim 3, said coil being printed on said frame.

6. In a miniature electrical indicating instrument of the moving coil type, as claimed in claim 3, said coil comprising electrically conductive wire wound on said frame.

7. In a miniature electrical indicating instrument of the moving coil type, as claimed in claim 1, said bracket means each including a second upstanding arm formed with a circular opening concentric with the axis of said frame, and each circular opening having a respective tongue extending thereinto; the relative lateral dimensions of said tongues and of said circular openings being such as to provide clearance for the rotation of said tongues in said circular openings with some degree of play.

8. In a miniature electrical electrical indicating instrument of the moving coil type, as claimed in claim 7, said extensions having laterally enlarged axially immediately inward of said second arms and engageable therewith to limit axial displacement of said moving coil frame responsive to external shocks.

9. In a miniature electrical indicating instrument of the moving coil type, as claimed in claim 5, said coil support frame being an open rectangle formed of light metal foil; said printed coil being electrically insulated from said frame.

10. In a miniature electrical indicating instrument of the moving coil type, as claimed in claim 6, said frame being an open rectangle formed of dielectric material.

11. In a miniature electrical indicating instrument of the moving coil type, as claimed in claim 1, a casing secured to said support base and enclosing the meter mechanism, said casing having a window in its outer surface extending longitudinally of the axis of said frame; and an indicator secured to said frame and extending in parallel spaced relation therewith longitudinally of said window, for movement in accordance with oscillations of said frame.

12. In a miniature electrical indicating instrument of the moving coil type, as claimed in claim 11, said frame comprising an open rectangle; said indicator including portions of magnetically neutral metal extending along the inner sides of those portions of the frame extending parallel to the axis thereof, and thus being positioned inwardly of the effective sides of the moving coil.

13. In a miniature electrical indicating instrument of the moving coil type, as claimed in claim 1, a receptacle secured to said support base adjacent an end of said frame; a viscious damping liquid in said receptacle; a substantially flat tongue extending from said frame radially of the axis thereof and into the viscous liquid in said receptacle; the inner dimensions of said receptacle being sufficiently small that the surface tension of the viscous liquid on said surfaces will inhibit loss of lisuid in any angular position of said coil. 7.

14. In a miniature electrical indicating instrument of the moving coil type, as claimed in claim 13, the interior of said receptacle being formed as a sector-shape slot 7 8 concentric with the axis of said frame and having a very 2,733,408 1/ 1956 Wakefield 324-154 small axial dimension. I Y 2,773,239 12/1956 Parker 324-150 15. In a miniature electrical indicating instrument of 2,840,767 6/ 1958 Ammon 324-451 the moving coil type, as claimed in claim 13, the surfaces 2,963,650 12/ 1960 Fisher 324151 of said tongue in contact with said viscous damping liq- 5 3,158,809 11/ 1964- Higley 324154 uid being of a material. which is notrwettable by the vis- 3,274,490 9/ 1966 Swanson 324-154 j m FOREIGN PATENTS 752,471 7/1956 Great Britain. 1,003,350 2/1957 Germany.

References Cited UNITED STATES PATENTS 641,051 1/1900 Stevens 324 154 X 10 1 1,130,633 3/1915 Roller 324-454 X RUDOLPH V. ROLINEC, Primary Examiner. 2,169,476 8/1939 lGill et a1 .3u-1s4 X 19, 9/1955 r y fin" 324 154 X GERARD R. STRECK-ER, Asszstant Exammer. 

